The United States Federal Railroad Administration has published statistics which indicate that train accidents caused by track failures including rail, joint bars and anchoring resulted in approximately 2700 derailments from 1992 to 2002. The primary cause of these track failures is a transverse defect and fissure running perpendicular to the rail running direction in the rail and rail bar joint.
A pair of rail joint bars holds the two ends of a rail in place and act as a bridge between the rail ends. The rail joint bars prevent lateral and vertical movement of the rail ends and permit longitudinal movement of the rails to accommodate expanding and contracting. Bolts extending through holes in the joint bars and the rail ends secure the rail ends together. Rail joint bars are typically 24 or 36 inches long with four or six bolt holes, respectively.
Various methods of rail inspection include magnetic, contact, ultrasonic and video. One such video system is the Automated Optical Joint Bar Inspection System developed by ENSCO, Inc. in cooperation with the Federal Railroad Administration. One such ultrasonic system is disclosed in U.S. Pat. No. 6,055,862 entitled “Method of and Apparatus for Detecting, Identifying and Recording the Location of Defects in a Railway Rail,” which is incorporated herein by reference.
One problem with video inspection systems is the inability to see into the rail joint bar and the area of the rail joint bar hidden under the head of the rail. Further, the most common failure of rail joint bars begins in an area centrally located within the bar. Video systems are also susceptible to false readings because of debris, rust and discoloration or streaks on the joint bar.
Ultrasonic testing of rails is performed with ultrasonic transducers housed in a liquid-filled wheel. The wheel rides along the top of the rail head while the transducers transmit ultrasonic waves into the rail head and receive reflected waves from the rail head. The orientation of the transducers and the wave path are used to identify defects in the rail head and web. However, the wave cannot pass from the rail head into the rail joint bar.